This invention relates to aqueous dispersions of peroxides useful in the curing of polyester resins and the suspension polymerization of vinyl monomers. In particular this invention relates to storage stable dispersions of normally solid organic peroxides which can contain high concentrations of the peroxide and are preferably sprayable and pumpable so as to make their use as initiators in the curing of unsaturated polyester resins and in the suspension polymerization of vinyl monomers more easily accomplished.
Peroxides have, as a general property, a tendency to be flammable and explosive with some peroxides exhibiting such properties to a greater extent than others. For example, benzoyl peroxide may decompose when dry due to shock, friction, or static electricity. This property carries with it the obvious hazards to the users of these materials as well as to the manufacturers and intermediate handlers thereof. One particularly burdensome aspect of this property occurs during shipment of the peroxides. Accordingly, it has long been an object to provide flame resistant organic peroxide compositions. For example, U.S. Pat. No. 3,507,800 is directed to providing a flame resistant peroxide composition consisting essentially of three components--water, peroxide and solvent wherein the water is at least about 18 percent of the composition.
The safety and end-use advantage provided by a water-soluble or a water emulsifiable initiator is well recognized. In this regard, U.S. Pat. No. 3,825,509 describes a process for the suspension polymerization of vinyl chloride wherein the initiator is an aqueous emulsion of an organic peroxide in which the peroxide is present in an amount up to 19 weight percent. The surfactant used to prepare the aqueous peroxide emulsion is a combination of polyvinyl alcohol and polyoxyethylene sorbitan monolaurate. However, emulsions containing greater than about 19 percent by weight of organic peroxide are described as being too viscous and therefore difficult to handle.
Providing an aqueous emulsion of a highly reactive organic peroxide, in and of itself, is not a guarantee of a safe product, as phase separation can result in a concentrated mass of undiluted organic peroxide. Decomposition of such an undiluted mass of organic peroxide, depending on such things as the total mass, container, temperature of decomposition, etc., can result in a decomposition that is accompanied by the liberation of heat and flammable gasses. Such conditions can lead to fires, deflagrations, pressure ruptures and detonations. Further, irrespective of any hazards, phase separation of the initiator emulsion can result in nonuniform concentrations of the initiator being supplied to the polymerization system. Efforts to provide a stable aqueous dispersion of organic peroxide include U.S. Pat. No. 3,988,261 which is directed to frozen aqueous emulsions of organic peroxides having a moderate to high concentration of organic peroxides. It has been suggested that such emulsions can be frozen without separation of the organic peroxide phase and water phase and, when thawed, retain their emulsified state at least for a period of time sufficient to allow safe handling and use. Although the frozen emulsified peroxide compositions of U.S. Pat. No. 3,988,261 may provide advantages for the handling of highly reactive peroxides, it is necessary for the end-user to provide special equipment for handling would be even more desirable to provide a pumpable product which can be shipped and forwarded directly from on-sight storage to the polymerization vessel.
There have been attempts in the past to make such dispersions. U.S. Pat. Nos. 4,039,475 and 4,092,470 disclose stable, pumpable aqueous suspensions of organic peroxides using a mixture of a) nonionic emulsifiers having a maximum HLB value of 12.5 and b) nonionic emulsifiers having a minimum HLB value of 12.5 or anionic emulsifiers. U.S. Pat. No. 4,734,135 discloses aqueous suspensions of solid organic peroxides using a protective colloid, a surface active agent and water. U.S. Pat. No. 4,440,885 teaches emulsions of a solid organic peroxide using an emulsifier having an HLB value from about 9 to about 20, hydrocarbon solvent and water.
Numerous other dispersions of solid organic peroxides are to be found in the art. Yet there is still a need for aqueous dispersions containing high concentrations of solid organic peroxides that are storage stable and preferably sprayable or pumpable.
It is therefore an object of the present invention to provide stable aqueous dispersions of normally solid organic peroxides.
Another object of the present invention is to provide high concentration dispersions of normally solid organic peroxides.
Also an object of the present invention is to provide dispersions of normally solid organic peroxides by the use of readily available components and equipment.
Another object of the present invention is the provision of dispersions of normally solid organic peroxides useful for the suspension polymerization of vinyl monomers.
Also an object of the present invention is the provision of dispersions of normally solid organic peroxides useful for curing polyester resin.
Still another object of the present invention is to provide sprayable or pumpable high concentration peroxide dispersions.
Other objects will become apparent from the following description.